Comment on "Force-field functor theory" [arXiv:1306.4332]

This comment regards a recently published preprint by R.Babbush, J.A.Parkhill, and A.Aspuru-Guzik, arXiv:1306.4332.Comment: 2 page

Almost-dispersionless pulse transport in long quasiuniform spring-mass chains: A new kind of Newton's cradle

Almost-dispersionless pulse transfer between the extremal masses of a uniform harmonic spring-mass chain of arbitrary length can be induced by suitably modifying two masses and their spring's elastic constant at both extrema of the chain. It is shown that a deviation (or a pulse) imposed to the first mass gives rise to a wave packet that, after a time of the order of the chain length, almost perfectly reproduces the same deviation (pulse) at the opposite end, with an amplitude loss that is as small as 1.3 % in the infinite-length limit; such a dynamics can continue back and forth again for several times before dispersion cleared the effect. The underlying coherence mechanism is that the initial condition excites a bunch of normal modes with almost equal frequency spacing. This constitutes a possible mechanism for efficient energy transfer, e.g., in nanofabricated structures.Comment: 16 pages, 10 figures, 2 table

Newton's cradle analogue with Bose-Einstein condensates

We propose a possible experimental realization of a quantum analogue of Newton's cradle using a configuration which starts from a Bose-Einstein condensate. The system consists of atoms with two internal states trapped in a one dimensional tube with a longitudinal optical lattice and maintained in a strong Tonks-Girardeau regime at maximal filling. In each site the wave function is a superposition of the two atomic states and a disturbance of the wave function propagates along the chain in analogy with the propagation of momentum in the classical Newton's cradle. The quantum travelling signal is generally deteriorated by dispersion, which is large for a uniform chain and is known to be zero for a suitably engineered chain, but the latter is hardly realizable in practice. Starting from these opposite situations we show how the coherent behaviour can be enhanced with minimal experimental effort.Comment: To appear in Journal of Physics

Effective potential approach to quantum dissipation in condensed matter systems

The effects of dissipation on the thermodynamic properties of nonlinear quantum systems are approached by the path-integral method in order to construct approximate classical-like formulas for evaluating thermal averages of thermodynamic quantities. Explicit calculations are presented for one-particle and many-body systems. The effects of the dissipation mechanism on the phase diagram of two-dimensional Josephson arrays is discussed.Comment: 7 pages, 5 figures, to appear in the Proceedings of Nonlinearity, Integrability And All That 20 Years After Needs 7